Petroleum, mining, geothermal, and other cutting bits have a fixed cutter attachment called a cutter assembly. The cutter assembly is attached to a rotatable drill bit head. The drill bit head is attached to a threaded pin used to attach the drill bit to a drill string assembly. The drill string assembly is rotated and weight is applied to the drill bit. The cutter assembly drags on the bottom of the hole and shears the rock producing rock cuttings. The cuttings are removed from the face of the drill bit by drilling fluids directed across the face of the drill bit, usually with one or more nozzles.
The cutter assembly needs to be extremely wear resistant. One technique is to form the assembly from synthetic very hard material, such as diamond, joined to a rigid tungsten carbide support. The diamond component can be attached to the tungsten carbide component by brazing. A braze filler interlayer is positioned between the diamond component and the tungsten carbide component. The interlayer is melted and upon subsequent solidification is bonded to the diamond component and to the tungsten carbide component forming a braze joint.
Bulk area heating, such as furnace heating, has been used to join cutter assembly components. All components are heated slowly to around 800.degree. C. and melted to form a material that has a liquid, or a mixture of liquid and solid parts. When melted, the braze interlayer wets the substrates to be joined and adheres to both the diamond component and the tungsten carbide component. This heating technique is non-selective, meaning that the entire element is heated uniformly. Average shear strength levels of 138 Mpa to 207 Mpa (20,000 to 35,000 psi) are possible by using non-selective heating methods.
However, during high temperature drilling conditions, the performance of drill bits produced by non-selective heating is limited. Dramatic reduction of the shear strength in the braze joint between the diamond cutting component and the support substrate occurs at high temperatures. As a result, drill bits are likely to fail at temperatures exceeding 700.degree. C. Thus, a method that produces a diamond cutter with a stronger braze joint leading to an improved shear strength at higher temperatures is desired.